Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
United States statutory tax rate	35.00%	21.00%	21.00%
Cash and cash equivalents held by foreign subsidiaries		$ 5,800
Temporary difference related to undistributed earnings		11,600	$ 12,900
Unrecognized tax liabilities		0	0
Valuation allowance against net deferred tax assets		4,882	964
United States
Income Taxes [Line Items]
Net operating loss, carryforwards		51,000			$ 28,300
Net operating loss, carryforwards expiration year					2028
Tax Cuts And Jobs Act Of 2017, change in tax rate income tax expense benefit				$ 22,700
Valuation allowance against net deferred tax assets		25,700	20,800
Canada
Income Taxes [Line Items]
Net operating loss, carryforwards		$ 16,800
Net operating loss, carryforwards expiration year		2033
Valuation allowance against net deferred tax assets		$ 5,600	$ 5,300
Russia
Income Taxes [Line Items]
Net operating loss, carryforwards		$ 1,100
Net operating loss, carryforwards expiration year		2026
Valuation allowance against net deferred tax assets		$ 200